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Topic: Multipath

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	Multipath - Wikipedia, the free encyclopedia
		In telecommunication, multipath is the propagation phenomenon that results in radio signals' reaching the receiving antenna by two or more paths.
		Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from terrestrial objects, such as mountains and buildings.
		The effects of multipath include constructive and destructive interference, and phase shifting of the signal.
	en.wikipedia.org /wiki/Multipath (299 words)

	Tutorial: Multipath (Site not responding. Last check: 2007-10-21)
		Multipath will cause amplitude and phase fluctuations, and time delay in the received signals.
		One such type of reduction is called the multipath fading; the phenomenon is known as "Rayleigh fading" or "fast fading." A representation of Rayleigh fading and a measured received power-delay profile are shown in Figure 2.
		A common measure of multipath delay spread is the root mean square (rms) delay spread.
	users.ece.gatech.edu /~mai/tutorial_multipath.htm (367 words)

	David Mann Audio FAQ -- FM Multipath
		"Multipath" is a phenomenon that, to a degree, affects all radio communications.
		Multipath can be caused by a variety of sources including: buildings, mountains, bridges, tall towers, passing airplanes or clouds, and windmills.
		The tuner's plight under a barrage of multipath is similar to your own while trying to understand voice announcements in a large transportation terminal filled with echoes.
	www.davidmannaudio.com /faq/faq5a.html (321 words)

	Multipath (Site not responding. Last check: 2007-10-21)
		Multipath in the radio channel creates; rapid changes in the signal strength over a small travel distance, or time interval; random frequency modulation due to varying doppler shifts on different multipath signals; and time dispersion caused by multipath propagation delays.
		Multipath propagation- the presence of reflecting objects and scatterers in the channel creates a constantly changing environment that dissipates the signal energy in amplitude, phase, and time.
		In flat fading, the multipath structure of the channel is such that the spectral characteristics of the transmitted signal are preserved at the receiver.
	home.gci.net /~raff242/fading.html (854 words)

	Multipath Mitigation - GPS World
		Multipath refers to the existence of signals reflected from objects in the vicinity of a receiver's antenna that corrupt the direct line-of-sight signals from the GPS satellites, thus degrading the accuracy of both code-based and carrier phase–based measurements.
		Particularly difficult is close-in multipath in which the reflected secondary signals arrive only slightly later (within about 100 nanoseconds) than does the direct-path signal, having been reflected from objects only a short distance from the receiver antenna.
		The authors demonstrated that significant reduction in multipath error can be achieved by using a receiver bandwidth much wider than was in current practice at that time, coupled with a significantly smaller spacing between the early and late correlator reference waveforms in the code-tracking loops.
	www.gpsworld.com /gpsworld/article/articleDetail.jsp?id=61316 (1001 words)

	Wireless
		Multipath tends not to be an issue because the transmission distances are less and because most of the multipath energy is absorbed by the physical environment.
		Multipath is the composition of a primary signal plus duplicate or echoed images caused by reflections of signals off objects between the transmitter and the receiver.
		The multipath channel from both the front (desired) antenna and the rear (undesired) antenna must be the same so that the fading from the desired and undesired antennae must be highly correlated.
	www.cisco.com /univercd/cc/td/doc/cisintwk/ito_doc/wireless.htm (13180 words)

	Multipath a Potential WLAN Problem
		Multipath propagation occurs when an RF signal takes different paths when propagating from a source (e.g., a radio NIC) to a destination node (e.g., access point).
		Multipath delay causes the information symbols represented in an 802.11 signal to overlap, which confuses the receiver.
		As examples, 802.11 signals in homes and offices may encounter 50 nanoseconds multipath delay while a manufacturing plant could be as high as 300 nanoseconds.
	www.wi-fiplanet.com /tutorials/print.php/1121691 (843 words)

	Pseudorange- and Carrier Phase Multipath
		Remaining errors are: twice the ionospheric error, pseudorange multipath error, carrier phase multipath error, receiver pseudorange noise, receiver carrier phase noise and the carrier phase ambiguity.
		However, this form of multipath is only important to users who want to use the receiver in the differential carrier mode (with one or more reference receivers) and thus determine position differences (or 'baselines') to the cm, or even mm level.
		If we assume the multipath contribution of the reference satellite for both receivers low (a reasonable assumption since only low elevation (less than 40 deg) satellites may show significant multipath), the residual is largely made up by the multipath of the 'normal' receiver's carrier phase measurement to the other (not the reference) satellite.
	home-2.worldonline.nl /~samsvl/multipat.htm (830 words)

	Multipath (Site not responding. Last check: 2007-10-21)
		In facsimile and television transmission, multipath causes jitter and ghosting.
		Decentralized Multiuser Detection For Time-Varying Multipath Channels The author (Sayeed Kadous) proposes an integrated framework based on canonical multipath-Doppler coordinates that exploits channel dispersion effects for MAI suppression.
		Xena, Warrior Princess: A Multipath Adventure The adventures of Xena: Warrior Princess come to 3D animation in new mulipath storylines.
	www.serebella.com /encyclopedia/article-Multipath.html (269 words)

	[No title] (Site not responding. Last check: 2007-10-21)
		The multipath term simply means that a host can access a LU by multiple paths, the path being a route from one host HBA port to one storage controller port.
		This tool ensure the multipath maps are always up-to-date with the fabric topology, and this ensure optimal performance by adding new paths to the existing maps as soon as they become available.
		All multipath hardware you will use must be described in either the config file if you have one, or the code defaults table if not, for the multipath tool to work.
	christophe.varoqui.free.fr /multipath.html (2518 words)

	Multipath and Diversity [Wireless, LAN (WLAN)] - Cisco Systems (Site not responding. Last check: 2007-10-21)
		Multipath distortion is a form of RF interference that occurs when a radio signal has more than one path between the receiver and the transmitter.
		Multipath delay causes the information symbols represented in 802.11 signals to overlap, which confuses the receiver.
		The purpose of diversity is to overcome multipath reflections.
	www.cisco.com /en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml (2232 words)

	LWN: Kernel Summit: Multipath I/O
		The big area of interest is multipath I/O. In the past, the kernel has suffered from multiple, incompatible multipath implementations at various levels in the source.
		Multipath hardware is full of undocumented protocols and proprietary software; it is not always easy to get the information needed to write a proper free driver for it.
		It is also hard to get at the hardware itself; multipath storage systems tend to be very expensive and aren't something that most developers, or even their employers, can just run out and buy.
	www.lwn.net /Articles/94569 (335 words)

	Multipath (Site not responding. Last check: 2007-10-21)
		With multipath, the signal path lengths are unequal, which results in several time delayed copies of the information signal arriving at the receiver.
		A worst case scenario would be wideband multipath where the received signal is spread so much that the receiver detects the spread parts of the signal as phase transitions.
		However, if the multipath is inconsistent (which may be the case with mobile users) the problem may be more pronounced and the information may need to be re-transmitted.
	www.qsl.net /n9zia/wireless/multipath.html (227 words)

	Multipath Signals: How do they make my GPS have errors? (Site not responding. Last check: 2007-10-21)
		Sometimes GPS wanderings caused by multipath can cause your GPS to "jump" from one position to another as the multipath signal "comes and goes" and causes your GPS to jump from using one group of erroneous signals to another.
		EVEN IF you have a clear sky view, multipath is possible, but the possibility of multipath errors are at least minimized with a clear sky view since it is probable that the GPS will have more than the minimum 4 satellites in view and can perhaps throw out the "bad" measurements.
		These multipath errors are just the nature of the technology at this point.
	www.gpsinformation.net /multipath.htm (468 words)

	Understanding Terrestrial Multipath Fading Phenomena
		Multipath signal fading can take on a variety of forms; by knowing its nature, it is possible to develop equalization and modulation approaches to minimize loss of transmitted information.
		The simplest measure of multipath is the overall time span of path delays from the first pulse to arrive at the receiver (the bona fide direct signal) to the last pulse to arrive at the receiver (the multipath echo).
		If the multipath signal, a, is equal to a(t), the multipath function is time dependent, as would be prevalent for a mobile communications receiver.
	www.mwrf.com /Articles/ArticleID/7964/7964.html (1319 words)

	Multipath fading generator aids wireless tests: News from Yokogawa Measurement Technologies
		As a result, when the receiver is moving, the reception signal receives amplitude and phase fluctuations, which are referred to as multipath fading.
		The multipath fading generator software can simulate two models: one where time-delay differences can be ignored, and one where they cannot.
		In the case of multipath fading in which the time delay difference cannot be ignored, the frequency characteristics of the reception signal changes.
	www.electronicstalk.com /news/yoa/yoa114.html (488 words)

	Definition: multipath (Site not responding. Last check: 2007-10-21)
		multipath: The propagation phenomenon that results in radio signals' reaching the receiving antenna by two or more paths.
		Note 2: The effects of multipath include constructive and destructive interference, and phase shifting of the signal.
		Note 3: In facsimile and television transmission, multipath causes jitter and ghosting.
	www.its.bldrdoc.gov /fs-1037/dir-023/_3424.htm (85 words)

	Multipath Interference (Site not responding. Last check: 2007-10-21)
		Multipath (often called picket fencing or flutter) happens when FM signals bounce around between the buildings in a city, or other large obstructions, this bounce causes a reflection and your FM radio tries to lock onto the original signal as well as the reflection!
		To identify multipath first try the AM radio and make sure the AM is strong, if the antenna has any problems they will usually cause the AM to be terrible or weak.
		To get rid of multipath static may not be easy, most folks would rather live with it than go to a lot of trouble to get rid of it.
	www.teamrocs.com /technical/pages/multipath.htm (431 words)

	[No title]
		However, the study concludes that the multipath reception problems identified by Sinclair are solvable with improved adaptive equalizer performance and that a well-designed 8-VSB receiver should be able to provide satisfactory reception at the Sinclair locations.
		COFDM avoids interference from multipath echoes by increasing the length of the signal samples, so that it is greater than the temporal spread of the multipath, and by applying a "guard interval" between data symbols where the receiver does not look for information.
		In particular, significant multipath components were found at 8 dB at 0.5 ms, -14 dB at +0.5 ms, -16 dB at +0.8 ms, -25 dB at +9.5 ms, with additional multipath components from 25 to 30 dB at +2 to +5 ms and at about 30 dB at +10 to +13ms.
	www.fcc.gov /Bureaus/Engineering_Technology/Documents/reports/dtvreprt.txt (9548 words)

	RFC 2991 (rfc2991) - Multipath Issues in Unicast and Multicast Next-Hop Se (Site not responding. Last check: 2007-10-21)
		The effect of multipath routing on a forwarder is that the forwarder potentially has several next-hops for any given destination and must use some method to choose which next- hop should be used for a given data packet.
		Two additional features are desirable: Minimal disruption When multipath is used, meaning that multiple routes contribute valid next-hops, the chances are higher of routes being added and deleted from consideration than when only the "best" route is used (in which case metric changes in alternate routes have no effect on traffic paths).
		Since a higher number of routes may actually be used for forwarding when multipath is in use, the potential for packet reordering and packet loss due to route flaps can be much greater than when not using multipath.
	www.faqs.org /rfcs/rfc2991.html (2148 words)

	GPS Code and Carrier Multipath Mitigation Using a Multiantenna System (Site not responding. Last check: 2007-10-21)
		Multipath is a major source of error in high precision Global Positioning System (GPS) static and kinematic differential positioning.
		Multipath accounts for most of the total error budget in carrier phase measurements in a spacecraft attitude determination system.
		From the multipath parameters, the code range and carrier phase multipath is estimated and compensated.
	www.ewh.ieee.org /soc/aes/taes/aes371/3710183.htm (304 words)

	GPSoft - SatNav Toolbox - Multipath (Site not responding. Last check: 2007-10-21)
		Multipath is the dominant error source in differential GPS (DGPS).
		The traditional technique used to isolate pseudorange multipath is referred to as "code-minus-carrier." The result of the procedure is illustrated here.
		The high frequency components are typical of thermal noise but the low frequency behavior is characteristic of multipath.
	www.gpsoftnav.com /multipath.html (73 words)

	[No title]
		Development of "Hercules" and "Xena" Multipath Movies is anticipated to commence this year, with distribution projected for fourth quarter '98.
		Each Multipath Movie runs approximately the same length as a film or video, with changes in plot being made based upon desired moods and profiles chosen for each character by the viewer.
		Multipath Movies utilize proprietary, technologically advanced software tools to produce three-dimensional, digitally animated stories, each with hundreds of plot alternative, or paths, that lead to multiple distinct conclusions that are influenced by the user.
	www.ausxip.com /articles/prnewswire1097.txt (544 words)

	Digital Transmission on Fading Multipath Channels - Tutorial - Development Library - National Instruments
		In this case, there is a received signal component that arrives via the direct path and an ensemble of secondary paths that are reflected from the ground terrain.
		A shallow-water acoustic channel is generally characterized as a multipath channel due to acoustic signal reflections from the surface and the bottom of the sea.
		A general model for a time-variant multipath channel is illustrated in Figure 10.4.
	zone.ni.com /devzone/conceptd.nsf/webmain/A4792F204D85239E86256DF90061D5F5 (3557 words)

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